[Webkit-unassigned] [Bug 51262] WebPageProxy should delete its backing store after not painting for a while

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=51262





--- Comment #36 from Adam Roben (aroben) <aroben at apple.com>  2011-02-14 07:52:56 PST ---
(In reply to comment #33)
> I) Transform the "sequence number" into a "state ID", and move control of the state ID to the UI process
> DrawingAreaProxyImpl would be in charge of incrementing the state ID whenever the state (i.e., size) changes. The new state ID would be passed to the web process in the SetSize message, and DrawingAreaImpl would store the state ID. DrawingAreaImpl would then pass its stored state ID back to the UI process the same way the sequence number is currently passed.

When resized, DrawingAreaProxyImpl currently keeps around the old backing store until the web process sends back a DidSetSize message. This is beneficial in the following circumstance:

1) View is resized in the UI process
2) DrawingAreaProxyImpl sends a SetSize message to the web process
3) DrawingAreaProxyImpl processes some already-sent Update messages from the web process (this step is optional)
4) The view asks DrawingAreaProxyImpl to paint something
5) DrawingAreaProxyImpl waits 0.5 seconds for the web process to send a DidSetSize message, doesn't get one, and draws the contents of the old backing store into the view

Keeping around the old backing store allowed us to draw it into the view when the web process was taking a long time to respond, and to update it with new content that was drawn by the web process before it received our SetSize message.

We should probably preserve this behavior, which means that we should send m_stateID+1 in the UpdateState message, and then set m_stateID to the ID passed back to us in the DidUpdateState message.

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